The surprise star of Wednesday’s celebration of female athletes? A 54-year-old grandfather.

Not just any grandfather, of course: We’re talking about Cornell McClellan, the super enthusiastic personal trainer of the president, first lady and their daughters. Yup, he’s the guy responsible for the first lady’s famously toned arms.

“They lead by example,“ McClellan said at the Capitol Hill celebration of National Girls and Women in Sports Day. “The White House is full of energy. The first family is definitely walking, running and skipping the talk.”

The Chicago fitness consultant started working with Michelle Obama 14 years ago; her husband became a client three years later. Now McClellan commutes to D.C. three or four times a week for workouts at the White House with the first family — and as many staffers as they can coax into the early morning sessions.

Yo-Yo Ma and the president with first lady Michelle Obama — check out her arms toned and buffed by personal trainer Cornell McClellan — at the Kennedy Center Honors in December. (Jacquelyn Martin?AP) “It’s important to them,” he told us. His best performer: The first lady, who he calls a “dynamo when it comes to fitness and being active. And her daughters know that and are following suit.” The president does the best he can; his “job is just so enormous that he can’t devote all the time he would like to working out. . . He works out daily, but if he’s got to leave early, he’s got to leave early.”

As a member of the President’s Council on Fitness, Sports & Nutrition, it’s McClellan’s job to get all Americans moving. With two daughters and two granddaughters, his message Wednesday was the value of sports for girls — a big topic in 2012, the 40th anniversary of Title IX. Girls playing any sport, he said, leads to better grades, better health, better jobs and the ability to stand up for themselves.

Never missing an opportunity to get people on their feet, he opened Wednesday’s briefing at the Rayburn Building by leading the crowd — including athletes Sarah Hughes, Grete Eliassen, Donna de Varona and Benita Fitzgerald Mosley — in a short routine of stretches, lifts and squats. “Let’s do a couple more,” he said to groans from the audience. He flashed a big smile. “Excellent!” (“I am tough,” he told us later. “But I always say to be people that I’m politely tough. So I work them very, very hard — but say please and thank you.”)

In case you’re wondering: Yes, you can hire McClellan as your personal trainer— if he can squeeze you into his schedule here or in Chicago. His rate is about $60-an-hour (“it varies”) and he tries to team up workout buddies to accommodate more clients.

We were curious: Who’s in better shape — desk-bound Washingtonians or meat-and-potatoes Chicagoans? McClellan has clearly learned the language of political diplomacy: “I think they all put forth a great effort.”